Method of making resistance material.



E. WEINTRAUB. METHOD OF MAKING RESISTANCE MATERIAL. APPLICATION FILED 00T.5, 1910.

1,019,568. Patehted Mar. 5, 1912.

W TNESSES. .ZiKZS/ENTUH J M EZEGA/YEL I/YEJNTHA'UB,

H25 AT TDHNE'YI UNITED STATES OFFICE.

EZECHIEL WEIN'I'BAUB, OF LYNN, MASSACHUSETTS, ABBIGNOR '10 GENERAL ELEC- TBIC COMPANY, A CORPORATION OF NEW YORK.

HE'I'HOD O1? a w aasrs'ranca MATERIAL.

To all whom it may concern:

Be it known that I, EZECHIEL Wsmraaun, a citizen of the United States, residing at Lynn, county of Essex, State of Massachusetts, have invented certain new and useful Improvements in Methods of Making Re sistance Material, (division of m application filed October 27, 1909, S erial No. 524,941,) of which the following is a specification.

My resent invention relates to resistances suitabe for use in electrical systems, and comprises a process formaking resistances consisting in arge part of boron or a boron com ound.

T e accompanying drawing illustrates one form of resistance stick made according to my present invention.

For man years it has been known that boric anhy rid could be reduced with magnesium to yield a compound rich in boron, but containin magnesium as an essential com onent. oissan attempted to improve on t is process and obtain boron free from magnesium, and to this end, decreased the proportion of magnesium in the reaction mixture. Former ex erimenters had used two parts boric anhv rid by weight to one of magnesium, an obtained magnesium borid. Moissan used three parts boric anhydrid to one part magnesium, and obtained after purifying his product what he called pure boron. He describes it as bein a brownish powder, practically non-c0n urlive for electricity, and va orizable without fusion. I am convinced tiat this material is not pure boron, but is in fact a boron suboxid associated with more or less magnesium borid. This I have established by analyses and tests, which need not here be recited in detail. I have found that pure boron is quite a different material, and I have discovered how to produce it in large quantities, and I have investigated its characteristics, and have conceived for it several industrial applications.

I have discovered that pure boron can be fused, and that it has a ne ative temperature coeiiicient of a magnitude without precedent. I find that boron, when changing in temperature from room temperature to 400 degrees 0., drops in resistance accord,-

Bpceiiloation of Letters Patent.

Original application filed October 87, 1909, Serial No. 6%,941.

Patented Mar. '5, 1912.

Divided and this application filed October 6,

Serial Ho. 585,389.

ing to the ratio of approximately two millions to one. I know of no element or compound even approaching in magnitude this enormous change in resistance in the interval of temperature mentioned. In the present application I have shown how this discovery may be made useful in the arts by the construction of resistance sticks or elements in which the temperature coefficientis negative, and of great magnitude, because of the preponderating influence of the boron present in the stick either in its elemental state or combined with carbon, silicon, or another chemical element.

(Zurc boron has a relatively high ohmic r istance, and although useful as a resistance material, can be greatly improved for many purposes by the addition of carbon. The percentage of carbon may vary through wide limits, its function being to decrease an otherwise high initial resistance while simultaneously c ntrolling the negative temperature coe cent.

Starting with boric anhydrid, I reduce this with magnesium in well-known manner, and then compress the resultant powder into a. stick. I next heat the stick in an Arsem vacuum furnace of the type shown in United States Patent No. 785,535, of March 21, 1905, where the stick not only gives u the impurities with which it iscom ose but also takes u some carbon from tie vapors normally given oil by the graphite heater of the furnace when operating at a temperature in the neighborhood of 2000 degrees C. The furnace should be heated up gradually and kept at the high temperature a long time. If the carbon taken up in this manner is not suflicient for the purpose in hand, enough carbon can be added to the magnesium borid owder before the powder is pressed into stick form. The amount of caron to be introduced varies with the use to which the sticks are to be applied. In case of motor starting resistances, a lar e negative temperature coefiicient is desira le, and the percentage of carbon will be small, say between a few tenths of a er cent. or five and six per cent. If the resistance sticks are to be used for lightning arrester resistances, the percentage of carbon may with advan tage be as high as ten per cent. With these pro rtions the temperature coefieient is smal while the specific resistance is still considerable.

As a modified method of building up the resistance sticks, I find that 1 can start with borie anh drid and reduce with carbon, bein care 111 that the anhydrid is in excess of t e carbon. The reduction product is then ground, pressed into sticks and finally sintered in an Arsem or other furnace.

As shown in the drawing, sticks 1 of boron, or boron associated with carbon, can with advantage be provided with iron terminals 2, madein the sha e ofrcaps and shrunk or fused to the ends of the stick. The sticks can be used as automatic motor starters, according to ;methods now well known, and the self-reducing characteristics of the stick will control automatically the supply of current to the motor. Thus, with a stick containing five per cent. carbon, one inch long and one quarter inch square, the resistance at room temperature is about 80 ohms, but on heating up to 800 degrees, the resistance progressively drops to about .08 ohms.

These self-reducing resistance sticks may be used not only as motor starters, but also as thermal cutouts for transformers, lam s and the like, according to methods ma e known in connection with other materials having ne ative temperature coefficients.

It will Es understood that the resistance material above described need not be in the form of a coherent stick, and can be used in other relations where its enormous negative emmas temperature coefiicient is of use in controlling the current, or in ma ifying the efiects of current variations, an the like.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The method which consists in reducing boric anhydrid with magnesium, adding carbon to the material thus produced, and heatin to free the material from substantially ali components except boron and carbon.

2. The method which consists in mixing carbon with impure boron, pressing into sticks, and heating to eliminate all components except the boron and carbon.

.3. The method of making resistances of boron associated with carbon which consists in sintering impure boron in the presence of carbon until only boron and carbon remain.

4. The method which consists in associ atim carbon with impure boron and heating to e iiminate impurities and to sinter the residue.

5. The method of making resistance bodies which consists in sintering impure boron in the presence of carbon.

6. The method of making resistance bodies which consists in mixing carbon with impure boron, pressing into shape, and heating to eliminate impurities and to sinter the residue.

In witness whereof, I have hereunto set my hand this third day of October, 1910.

EZECHIEL WEINTRAUB. Witnesses:

JOHN A. McMANUs, Jn, FRANK G. I'IAT'IIE. 

